Recently, a device of a miniaturized structure of a nanometric size, exemplified by a single molecule optical memory or a single electron device, is being put to practical use, on the basis of development of the fine processing technology. The near-field optical microscope, having a resolution of a nanometric size, is attracting attention as a technique indispensable for development and evaluation of such device. This near-field optical microscope detects the intensity, wavelength or polarization, for example, of emitted or propagated light from a specimen to help to give information on physical properties of the specimen from the emitted or propagated light from the specimen.
The near-field optical microscope includes an optical probe including in turn a core formed of optical fiber and a clad formed about the core. The core has a sharpened protrusion at its distal end, coated with metal, such as Au or Ag. With the near-field optical microscope, it is possible to obtain an optical image with a resolution beyond the wavelength of light. That is, with use of this near-field optical microscope, it is possible not only to measure physical properties of a minute region of a specimen with resolution of the order of nanometers, but also to perform memory operations, such as read or write, and even optical machining. The above optical probe, used in this near-field optical microscope, has already been disclosed.
In measuring the physical properties in the minute region of the specimen, with this near-field optical microscope, the evanescent light, localized in a surface region on the specimen, smaller than the light wavelength, is detected, in order to measure the shape of the specimen. This evanescent light, generated on irradiation of the specimen with light under total reflection conditions, is scattered by the above optical probe so as to be thereby converted into scattered light. The scattered light, obtained in this manner, is guided to the core of the optical fiber, through the protrusion of the optical probe, so as to be detected by a photodetector provided at the opposite side light radiating end of the optical fiber. Thus, it is possible with this near-field optical microscope to effect both scattering and detection by the optical probe including the protrusion.
Meanwhile, the above-described near-field optical microscope, enabling measurement with a high resolution, has a demerit that the measurement range is as narrow as tens of μm. On the other hand a laser microscope, employing usual propagated light, providing for broad range measurement, is inferior in resolution to e.g. a near-field optical microscope.
Moreover, the resolution of a near-field optical microscope is limited by the diameter of the aperture of the optical probe used, so that, in case the physical properties are measured as the resolution is changed, it is necessary that an optical probe for low resolution, different in the aperture diameter, be separately mounted on the near-field optical microscope. Thus, in switching to measurement with high resolution, exploiting near-field light, it is necessary to exchange the optical probes to be in use, as a routine operation, so that the user cannot be relieved of excess load. There also arises a problem that this leads to deviated positions of the optical probe, already adjusted, relative to the minute area, the physical properties of which are desired to be measured.